Over-fired furnace



Patented May 16, 1939 UNITED STATES PATENT OFFICE OVER-FIRED FURNACE Application November 17, 1937, Serial No. 175,123

3 Claims.

This invention relates to metal heating furnaces and particularly to an improved over-fired pit-type furnace for heat treating metal articles.

It is usually the practice to anneal, normalize or otherwise heat treat metal articles, such as wire and rod stock, by placing the bundles of material in a plurality of closed metallic heat boxes or containers, and placing the loaded boxes in the heating chamber of a conventional pittype furnace. In such furnaces, the firing usually takes place at the bottom of the furnace and the heat is directed to the base of the heating boxes. Such firing heats the lower part of the boxes by radiation and the upper part by convection from the waste gases as they pass upwardly through the furnace to an opening at the top thereof communicating with a flue or stack.

Heating furnaces of this type are difficult to control and do not heat the articles uniformly, usually overheating the material in the bottom of the boxes, which is very undesirable. Such furnaces, too, have the disadvantage that they can handle only a limited number of boxes at eone time, thereby limiting the rate of production in heating, and also, in such furnaces, usable heating gases are wasted up the stack, reducing the eiiciency.

It is an object of this invention to provide a furnace which will overcome these disadvantages and which, at the same time, is simple and inexpensive in its operation and construction.

It is another object of this invention to provide an improved over-fired heat treating furnace which uses the heating gases to the best advantage and which heats articles quickly and uniformly.

Various other objects and advantages of this invention will become more apparent during the course of the following specification, and will be particularly pointed out in the appended claims.

In the accompanying drawings I have shown, for the purpose of illustration, one embodiment which my invention may assume in practice.

In the drawings:

Figure 1 is a plan showing the improved overred furnace of my invention;

Figure 2 is a sectional view taken on the line IIII of Figure 1;

Figure 3 is a sectional View taken on the line III-III of Figure 1; and,

Figure 4 is a sectional view taken on the line IV-IV of Figure l.

There is shown in the drawings the over-fired furnace of my invention, which comprises a cooling chamber 2, a preheating chamber 3 and a main heating chamber 4, arranged side-by-side and open at the top. The preheating chamber is separated from the main heating chamber and from the cooling chamber by refractory walls 5 and 6, respectively. Each of the chambers is adapted to be closed by removable refractory lined covers 1. The main heating chamber has a longitudinally extending passageway or flue 8 in the bottom of the hearth thereof which is connected to a similar longitudinally extending passageway or flue 9 in the bottom of the hearth of the preheating chamber by means of a connecting ue I0 provided with a damper II. There is located outside the furnace at the end of the preheating chamber a main exit flue `I5 provided with a damper I6 which connects this chamber with a stack I4. There is also arranged outside the furnace, preferably at one side or end of the main heating chamber, a by-pass iiue I2 provided with a damper I3 which conneots the passageway or flue 8 in the main heating chamber with the stackV I4. The furnace is of the over-red type and is adapted to be heated at one end of the main heating chamber over the load therein by burners I1, and may be red by means of oil, gas, pulverized coal, coke, oven gas, producer gas, or some other suitable heating medium. The articles, such as bundles or coils, of wire or rod stock, are placed in suitable metallic heating boxes or containers I8 which are adapted, when placed on the hearth in the furnace, to straddle the flue or passageway in the main heating and preheating chambers.

The movement of the material through the furnace will now be described. It will be considered that the furnace is now in operation and that the heating boxes have just been transferred from the preheating chamber to the main heating chamber in the heating cycle. The boxes are heated in the main heating chamber to theproper temperature and then transferred to the cooling chamber, and the boxes in the preheating chamber transferred to the main heating chamber and the preheating chamber filled with cold heating boxes, and the cycle repeated. It will be understood, of course, that the covers 'I are placed in position to close each of the chambers during the heating,

The path of the heating or combustion gases is designated in the drawings by the arrows. Fuel is iired into one end of the heating chamber through the burners I'I and combustion takes place above the load therein. 'Ihe combustion gases in this chamber tend to move horizontally through the chamber down through and around the heating boxes therein into the flue br passageway 8 in the bottom of the hearth thereof. From there they travel to the connecting flue I0 into the passageway or flue 9 in the hearth of the preheating chamber up through and around the heating boxes therein, into the main ue I5, and out to the stack, primarily due to the stack draft.

The by-pass iiue I2 is normally closed by the damper I3, that is, when both the main heating and preheating chambers are used. When it is desired to use only the main heating chamber without the use of the preheating chamber, the connecting flue I0 is closed by means of the damper II and the damper I3 of the by-pass fiue I2 is opened. In this arrangement the combustion gases pass down through and around the heating boxes in the chamber into the flue 8 and out to the stack through the by-pass flue I2. It is not necessary that the hearths in the main heating chamber and the preheating chamber be provided with the passageways or ues 8 and 9, as they may be provided with flat hearths, but it is preferable that such passageways be provided in order to properlydirect the heating gases between and around the heating boxes in these chambers to obtain the best heating effects.

It is also desirable to provide a means for introducing suitable inert or protective gases into the heating boxes or containers while in the furnace to protect the material therein against oxidation and staining. 'I'his is preferably accomplished by providing a plurality of openings I9 in the outside Wall of the main heating chamber which are adapted to receive recessed heat resisting metal gas lances 26 which are suitably connected to the heating boxes in the main heating chamber to conduct the gases thereto.

It will be seen from this invention that I have provided a furnace wherein` the heating boxes in the heating chamber are subjected to an enveloping down-draft flame whereby they are rapidly and uniformly heated and that the hot gases passing along the fiues in the hearths heat the boxes in both the main heating and preheating chambers by convection.

While I have shown and described a specic embodiment of the present invention, it will be understood that I do not wish to be limited exactly thereto since various modifications may be made without departing from the scope of the invention, as defined by the following claims.

I claim:

l. An over-fired pit-type furnace for heating articles having a cooling, a preheating and a main heating chamber and a hearth in the bottom of each of said chambers, each of the hearths in said preheating and main heating chambers having a longitudinally extending interconnected ue passageway positioned in and below the bottom thereof, said articles to be heated adapted to straddle said flue when the furnace is charged, means for firing said furnace positioned at one end of the main heating chamber above the articles to be heated whereby the heating gases therein are adapted to pass over, down through and around said articles in said main heating chamber into the flue passageway at the bottom thereof, thence into the flue passageway at the bottom of the preheating chamber, under and up through and around the articles therein and out of the furnace.

2. An over-fired pit-type furnace having a cooling chamber, a preheating chamber and a main heating chamber, a longitudinally extending gas passageway in each of the preheating and main heating chambers, said passageways positioned in and below the hearths of said chambers, a flue gas passageway extending between the chambers connecting said passageways, and means positioned in the end wall of said main heating chamber above the articles to be heated for firing said furnace whereby said heating gases are adapted to pass down through and around the articles in the main heating chamber into the passageway in the bottom thereof, through the flue passageway between the chambers into the passageway in the bottom of the preheating chamber and up through and around the articles therein and out of the furnace.

3. An over-fired pit-type furnace having at least a preheating and main heating chamber, a heating gas passageway arranged in each of said chambers, said passageways being interconnected and positioned below the hearths of the chambers, and means positioned in one of the walls of the main heating chamber above the articles positioned therein to be heated for firing the furnace whereby the heating gases are adapted to pass down through and around the articles in the main heating chamber into the passageway therein and into the passageway in said preheating chamber and up through and around the articles therein,

PETER STEWART. 

